Arguments

the x and y co-ordinates to be used to position the legend.
They can be specified by keyword or in any way which is accepted by
xy.coords: See ‘Details’.

legend

a character or expression vector
of length ≥ 1 to appear in the legend. Other
objects will be coerced by as.graphicsAnnot.

fill

if specified, this argument will cause boxes filled
with the specified colors (or shaded in the specified colors)
to appear beside the legend text.

col

the color of points or lines appearing in the legend.

border

the border color for the boxes (used only if
fill is specified).

lty, lwd

the line types and widths for lines appearing in the
legend. One of these two must be specified for line drawing.

pch

the plotting symbols appearing in the legend, as
numeric vector or a vector of 1-character strings (see
points). Unlike points, this can all be
specified as a single multi-character string. Must be
specified for symbol drawing.

angle

angle of shading lines.

density

the density of shading lines, if numeric and
positive. If NULL or negative or NA color filling
is assumed.

bty

the type of box to be drawn around the legend. The allowed
values are "o" (the default) and "n".

bg

the background color for the legend box. (Note that this is
only used if bty != "n".)

box.lty, box.lwd, box.col

the line type, width and color for
the legend box (if bty = "o").

pt.bg

the background color for the points,
corresponding to its argument bg.

cex

character expansion factor relative to current
par("cex"). Used for text, and provides the default for
pt.cex.

pt.cex

expansion factor(s) for the points.

pt.lwd

line width for the points, defaults to the one for
lines, or if that is not set, to par("lwd").

xjust

how the legend is to be justified relative to the legend
x location. A value of 0 means left justified, 0.5 means centered
and 1 means right justified.

yjust

the same as xjust for the legend y location.

x.intersp

character interspacing factor for horizontal (x) spacing.

y.intersp

the same for vertical (y) line distances.

adj

numeric of length 1 or 2; the string adjustment for legend
text. Useful for y-adjustment when labels are
plotmath expressions.

text.width

the width of the legend text in x ("user")
coordinates. (Should be a single positive number even for a reversed
x axis.) Defaults to the proper value computed by
strwidth(legend).

text.col

the color used for the legend text.

text.font

the font used for the legend text, see text.

merge

logical; if TRUE, merge points and lines but
not filled boxes. Defaults to TRUE if there are points and lines.

trace

logical; if TRUE, shows how legend does all
its magical computations.

plot

logical. If FALSE, nothing is plotted but the
sizes are returned.

ncol

the number of columns in which to set the legend items
(default is 1, a vertical legend).

horiz

logical; if TRUE, set the legend horizontally
rather than vertically (specifying horiz overrides the ncol
specification).

title

a character string or length-one expression giving a
title to be placed at the top of the legend. Other objects will be
coerced by as.graphicsAnnot.

inset

inset distance(s) from the margins as a fraction of the
plot region when legend is placed by keyword.

xpd

if supplied, a value of the graphical parameter xpd
to be used while the legend is being drawn.

title.col

color for title.

title.adj

horizontal adjustment for title: see the help
for par("adj").

seg.len

the length of lines drawn to illustrate lty
and/or lwd (in units of character widths).

Details

Arguments x, y, legend are interpreted in a
non-standard way to allow the coordinates to be specified via
one or two arguments. If legend is missing and y is not
numeric, it is assumed that the second argument is intended to be
legend and that the first argument specifies the coordinates.

The coordinates can be specified in any way which is accepted by
xy.coords. If this gives the coordinates of one point,
it is used as the top-left coordinate of the rectangle containing the
legend. If it gives the coordinates of two points, these specify
opposite corners of the rectangle (either pair of corners, in any
order).

The location may also be specified by setting x to a single
keyword from the list "bottomright", "bottom",
"bottomleft", "left", "topleft",
"top", "topright", "right" and
"center". This places the legend on the inside of the plot
frame at the given location. Partial argument matching is used. The
optional inset argument specifies how far the legend is inset
from the plot margins. If a single value is given, it is used for
both margins; if two values are given, the first is used for x-
distance, the second for y-distance.

Attribute arguments such as col, pch, lty, etc,
are recycled if necessary: merge is not. Set entries of
lty to 0 or set entries of lwd to NA to
suppress lines in corresponding legend entries; set pch
values to NA to suppress points.

Points are drawn after lines in order that they can cover the
line with their background color pt.bg, if applicable.

See the examples for how to right-justify labels.

Since they are not used for Unicode code points, values -31:-1
are silently omitted, as are NA and "" values.

Value

A list with list components

rect

a list with components

w, h

positive numbers giving width and
height of the legend's box.

left, top

x and y coordinates of upper left
corner of the box.

text

a list with components

x, y

numeric vectors of length length(legend),
giving the x and y coordinates of the legend's text(s).